Center photodetector determination in a scintillation camera is an important function where the light intensity signals are to be analyzed digitally. It is known in the art to use analog comparators in order to determine whether a given photodetector in a planar array of photodetectors has a signal greater than its neighboring photodetectors. This results in the generation of a center photodetector signal, however, such an analog circuit does not indicate whether the center photodetector has the greatest intensity of all photodetectors in the array.
Furthermore, an analog scheme for intensity value comparison can only be successful if the gain of the photodetectors is accurately adjusted. Such a system is known from U.S. Pat. No. 5,309,357, in which there is also disclosed with reference to FIG. 3 thereof, the use of serial analog-to-digital converters for the intensity signals from each photodetector. When a first bit is received from the serial analog-to-digital converters, the photodetector first generating such bit is assumed to be at least near the center of the scintillation event. The data acquisition system then resets the analog-to-digital converters remote from a group of photodetectors surrounding the one detector whose serial analog-to-digital converter produced the first high value. The disclosed system improves conversion throughput but does not provide an accurate determination of which photodetector has received the greatest light intensity and can be considered the center tube. The system described in U.S. Pat. No. 5,309,357 determines which photodetector has the greatest intensity value within an order of binary magnitude.